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arXiv:2012.14606 · Physical Review A

Scalable hyperfine qubit state detection via electron shelving in the 2D5/2 and 2F7/2 manifolds in 171Yb+

Claire Edmunds, Ting Rei Tan, Alistair R. Milne, A. Singh, Michael J. Biercuk, Cornelius Hempel

Published Jul 19, 2021• 27 citations
arXivHTMLPDF

Abstract

Qubits encoded in hyperfine states of trapped ions are ideal for quantum computation given their long lifetimes and low sensitivity to magnetic fields, yet they suffer from off-resonant scattering during detection, often limiting their measurement fidelity. In ${}^{171}{\text{Yb}}^{+}$ this is exacerbated by a low fluorescence yield, which leads to a need for complex and expensive hardware, a problematic bottleneck especially when scaling up the number of qubits. We demonstrate a detection routine based on electron shelving to address this issue in ${}^{171}{\text{Yb}}^{+}$ and achieve a $5.6\ifmmode\times\else\texttimes\fi{}$ reduction in single-ion detection error on an avalanche photodiode to $1.8(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ in a 100 $\ensuremath{\mu}\mathrm{s}$ detection period and a $4.3\ifmmode\times\else\texttimes\fi{}$ error reduction on an electron multiplying CCD camera with $7.7(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ error in 400 $\ensuremath{\mu}\mathrm{s}$. We further improve the characterization of a repump transition at 760 nm to enable a more rapid reset of the auxiliary ${}^{2}{F}_{7/2}$ states populated after shelving. Finally, we examine the detection fidelity limit using the long-lived ${}^{2}{F}_{7/2}$ state, achieving further $300\ifmmode\times\else\texttimes\fi{}$ and $12\ifmmode\times\else\texttimes\fi{}$ reductions in error to $6(7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ and $6.3(3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ in 1 ms on the respective detectors. While shelving-rate limited in our setup, we suggest various techniques to realize this detection method at speeds compatible with quantum information processing, providing a pathway to ultrahigh-fidelity detection in ${}^{171}{\text{Yb}}^{+}$.

DOI
10.1103/physreva.104.012606

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Qubits encoded in hyperfine states of trapped ions are ideal for quantum computation given their long lifetimes and low sensitivity to magnetic fields, yet they suffer from off-resonant scattering during detection, often limiting their measurement fidelity. In 171Yb+{}^{171}{\text{Yb}}^{+}171Yb+ this is exacerbated by a low fluorescence yield, which leads to a need for complex and expensive hardware, a problematic bottleneck especially when scaling up the number of qubits. We demonstrate a detection routine based on electron shelving to address this issue in 171Yb+{}^{171}{\text{Yb}}^{+}171Yb+ and achieve a 5.6\ifmmode×\else\texttimes\fi5.6\ifmmode\times\else\texttimes\fi{}5.6\ifmmode×\else\texttimes\fi reduction in single-ion detection error on an avalanche photodiode to 1.8(2)\ifmmode×\else\texttimes\fi10\ensuremath−31.8(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}1.8(2)\ifmmode×\else\texttimes\fi10\ensuremath−3 in a 100 \ensuremathμs\ensuremath{\mu}\mathrm{s}\ensuremathμs detection period and a 4.3\ifmmode×\else\texttimes\fi4.3\ifmmode\times\else\texttimes\fi{}4.3\ifmmode×\else\texttimes\fi error reduction on an electron multiplying CCD camera with 7.7(2)\ifmmode×\else\texttimes\fi10\ensuremath−37.7(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}7.7(2)\ifmmode×\else\texttimes\fi10\ensuremath−3 error in 400 \ensuremathμs\ensuremath{\mu}\mathrm{s}\ensuremathμs. We further improve the characterization of a repump transition at 760 nm to enable a more rapid reset of the auxiliary 2F7/2{}^{2}{F}_{7/2}2F7/2​ states populated after shelving. Finally, we examine the detection fidelity limit using the long-lived 2F7/2{}^{2}{F}_{7/2}2F7/2​ state, achieving further 300\ifmmode×\else\texttimes\fi300\ifmmode\times\else\texttimes\fi{}300\ifmmode×\else\texttimes\fi and 12\ifmmode×\else\texttimes\fi12\ifmmode\times\else\texttimes\fi{}12\ifmmode×\else\texttimes\fi reductions in error to 6(7)\ifmmode×\else\texttimes\fi10\ensuremath−66(7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}6(7)\ifmmode×\else\texttimes\fi10\ensuremath−6 and 6.3(3)\ifmmode×\else\texttimes\fi10\ensuremath−46.3(3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}6.3(3)\ifmmode×\else\texttimes\fi10\ensuremath−4 in 1 ms on the respective detectors. While shelving-rate limited in our setup, we suggest various techniques to realize this detection method at speeds compatible with quantum information processing, providing a pathway to ultrahigh-fidelity detection in 171Yb+{}^{171}{\text{Yb}}^{+}171Yb+.
Abstract High-fidelity quantum state detection is essential for quantum information processing, yet in trapped-ion systems it is fundamentally limited by state leakage arising from off-resonant excitation during fluorescence detection. Here, we demonstrate a leakage-suppressed detection scheme for 171 Yb + qubits based on stateselective shelving to a metastable 2 D 3/2 manifold. This approach effectively suppresses population leakage and significantly enhances detection fidelity. We achieve an average detection fidelity of 99.88(2)%, representing a significant improvement over conventional methods. The scheme requires minimal additional experimental resources and is compatible with existing qubit-control configurations, supporting mid-circuit measurement in trapped-ion systems. With state-of-the-art total photon detection efficiency, a detection fidelity of 99.98% is projected, highlighting its potential for scalable quantum information processing.
We present two novel approaches to state detection of qubits defined with trapped ions. The first uses simple pulse sequences from a mode-locked laser to induce state-dependent excitations in less than 1 ns. The resulting atomic fluorescence occurs in the dark, allowing the placement of non-imaging detectors right next to the atom to improve the qubit state detection efficiency and speed.The second employs the long lived F state in Yb+ which has been used in quantum information science almost exclusively for clocks and optical-frequency qubits. We describe how this resource can be used in conjunction with the ground state S1/2 manifold to aid in the scaling of trapped ion quantum information science. Narrow-band optical pumping into the 2F7/2 from one of the conventional 2S1/2 qubit states is projected to achieve a higher state preparation and measurement (SPAM) fidelity than any other demonstrated technique.
The highly popular ytterbium-171 (171mathrmYb+^{171} \\mathrm{Yb}^+171mathrmYb+) ion is commonly employed in quantum information research as a qubit whose excellent coherence time and fast, simple state preparation has allowed cutting edge work in quantum computation and simulation. Despite these large benefits, the demonstrated measurement fidelity of this ion has lagged the state preparation and gate fidelity achieved to date.In this thesis we investigate and realize methods of increasing the measurement fidelity of 171mathrmYb+^{171} \\mathrm{Yb}^+171mathrmYb+ in a scaleable way for large quantum systems. Using methods of coherent control, we implement a pulsed state detection scheme using a mode-locked laser to perform background-free spectroscopy of the ``bright'' state of the qubit. The small hyperfine splitting of the ion necessitates the use of multiple (two) pulses to manipulate time dynamics of the ion to excite a single transition. A Mach-Zehnder interferometer is constructed to control these pulse separations both coarsely (sim\\simsim 237 ps) and on a fine sub-femtosecond scale. These pulses cause destructive/constructive interference of the electron wave packet of a single ion levitated in vacuum and are engineered to state-selectively excite the qubit. This allows measurement of the qubit whose transition frequency is much smaller than the bandwidth of the interrogation laser.During this spectroscopy, mechanical forces from the mode-locked laser frequency comb can drive the ion into large coherent states of motion. This motion has been dubbed ``phonon lasing''. We investigate the phonon lasing affect and how the ion interacts with multiple comb teeth. The large number of teeth leads to a protection mechanism from runaway energy gain by near-by blue detuned teeth, allowing ions to be trapped and cooled by the mode-locked laser, regardless of its detuning. We further explore these discrete amplitude coherent states by injecting energy into the ion's motion and exciting higher-order oscillations.We, for the first time, implement an ``electron shelving'' of the hyperfine qubit, and incoherently transfer the bright state population in the extremely long-lived ($\\approx$5 yr) 2^22F7/2_{7/2}7/2​ state of 171^{171}171Yb+^++, functionally disconnected state. This is accomplished via narrow-band optical pumping on the 2^22S1/2_{1/2}1/2​ to the 2^22D5/2_{5/2}5/2​ quadrupole which has a leaky dipole channel into the 2^22F7/2_{7/2}7/2​. Narrow-band optical pumping is again used to rescue the ion at the end of the experiment with the aid of a 760 nm E2 transition back into the cooling cycle. Measurement with this scheme is no longer limited by off-resonant effects from the main cycling transition. Limits of this novel technique, as well as further directions using the F state as a utility for quantum information are explored. Finally, we combine the pulsed background-free spectroscopy with shelving and demonstrate high-fidelity, background free detection of a single trapped 171mathrmYb+^{171}\\mathrm{Yb}^+171mathrmYb+ qubit.
Fluorescence of single, trapped 171Yb^{171}\mathrm{Yb}171Yb+{}^{+}+ ions has been experimentally studied as a function of laser polarization, power, and detuning and as a function of magnetic field strength. The suppression of efficient fluorescence by coherent population trapping and the counteracting effect of the magnetic field are found to agree with theoretical predictions. For comparison, a fluorescence study has also been made of the isotope 174Yb^{174}\mathrm{Yb}174Yb+{}^{+}+ for which coherent population trapping is absent on the main fluorescence and laser cooling transition. Finally, state-sensitive fluorescence detection of the 171Yb^{171}\mathrm{Yb}171Yb+{}^{+}+ hyperfine qubit is studied, including the role of coherent population trapping in the optimization of detection parameters. A qubit detection fidelity of greater than 9797%97 is achieved.
Abstract The recently demonstrated trapping and laser cooling of 133Ba+ has opened the door to the use of this nearly ideal atom for quantum information processing. However, before high-fidelity qubit operations can be performed, a number of unknown state energies are needed. Here, we report measurements of the 2P3/2 and 2D5/2 hyperfine splittings, as well as the 2P3/2 ↔ 2S1/2 and 2P3/2 ↔ 2D5/2 transition frequencies. Using these transitions, we demonstrate high-fidelity 133Ba+ hyperfine qubit manipulation with electron shelving detection to benchmark qubit state preparation and measurement (SPAM). Using single-shot, threshold discrimination, we measure an average SPAM fidelity of F=0.99971(3){\mathcal{F}}=0.99971(3)F=0.99971(3) F = 0.99971 ( 3 ) , a factor of ≈2 improvement over the best reported performance of any qubit.
Fast and efficient detection of the qubit state in trapped ion systems is critical for implementing quantum error correction and performing fundamental tests such as a loophole-free Bell test. In this work we present a simple qubit state detection protocol for a (171)Yb+ hyperfine atomic qubit trapped in a microfabricated surface trap, enabled by high collection efficiency of the scattered photons and low background photon count rate. We demonstrate average detection times of 10.5, 28.1, and 99.8 μs, corresponding to state detection fidelities of 99%, 99.856(8)%, and 99.915(7)%, respectively.